The flow of oil within a transmission is controlled in a manner to lubricate the moving components and to apply clutches when needed. Transmissions often include a case side cover pan having an oil chamber which stores oil that may be selectively delivered to an oil sump to provide desired levels of oil within the transmission. If the oil sump level is unnecessarily high, then the oil may interfere with the rotating components of the transmission as a result of the paddlewheel effect of the moving components rotating through the oil, or the viscous coupling effect of the oil on the rotating components. This interference causes spin losses which translate directly into reduced fuel economy.
The flow of oil from the oil chamber of the case side cover pan into the oil sump is typically controlled by a thermostatic element which is operative to reduce the flow of oil when the oil is above a predetermined temperature level. The thermostatic element contains a temperature sensitive strip of metal that reacts to fluid temperature changes to open or close a fluid passage. At low temperatures, the thermostatic element exerts little pressure on the thermostatic element plate, which allows fluid to drain into the sump. As the temperature of the fluid rises, the thermostatic element begins to apply pressure to the thermostatic element plate, thereby trapping fluid in the case side cover pan. This control is needed to maintain the operation of the hydraulic system. The thermostatic control element provides a passive control which may not be adjusted based upon operating conditions of the transmission or vehicle.